1. Field of the Invention
The present invention relates to an imaging device and an imaging system.
2. Description of the Related Art
As an example of a structure for speeding up an imaging device, there is known a structure including a first accumulation unit configured to hold signals output from pixels, a buffer unit configured to transmit the signals held by the first accumulation unit, and a second accumulation unit, to which the signals are transmitted from the buffer unit, as described in Japanese Patent Application Laid-Open No. 2009-089367. In the imaging device of Japanese Patent Application Laid-Open No. 2009-089367, the first accumulation unit first holds a signal of a first pixel. The buffer unit then transmits the signal of the first pixel held in the first accumulation unit to the second accumulation unit. Thereafter, the first accumulation unit holds a signal of a second pixel during a period, in which the signal of the first pixel is read out from the second accumulation unit. Thus, a period, in which the signal of the first pixel is read out from the second accumulation unit, and a period, in which the signal is output from the second pixel to the first accumulation unit, can be superposed. Therefore, speed-up of the imaging device can be realized in comparison to an imaging device having a structure without a second accumulation unit.
Japanese Patent Application Laid-Open No. 2004-134867 describes an imaging device, in which an amplifying element is shared by a plurality of photoelectric conversion unit and configured to output signals based on electric charges accumulated in the photoelectric conversion units to a vertical signal line. The amplifying element then outputs a first signal based on electric charges generated by a first photoelectric conversion unit and a second signal based on electric charges obtained by adding electric charges generated by the first photoelectric conversion unit and electric charges generated by another photoelectric conversion unit.
However, further speed-up of the operation is not considered in Japanese Patent Application Laid-Open No. 2009-089367 or Japanese Patent Application Laid-Open No. 2004-134867.